Temperature-regulated faucets are used, at least in some cases, to ensure that the water ejected from the faucet does not have a harmfully excessive temperature. Various methods have been used to carry this out, including the use of thermostatic valves that force inclusion of cold water in the ejected water if the water temperature is above a threshold.
Prior designs suffer many drawbacks, including lack of reliability, lack of easy adjustability, and manufacturing cost. For example, at least some building codes require the use of an ASSE 1070 mixing valve to insure outlet temperature never exceeds 110°. Currently, faucets meet this code by the use of an under-the-counter thermostatic mixing valve (TMV). The inherent flaw to this design is that the TMV is under constant pressure and relies on independent spring check valves to prevent a cross connection within the plumbing system. In other words, failure or degradation of the under-the-counter mixing valve can affect the plumbing system, as opposed to merely resulting in poor operation of the faucet.
Furthermore, spring check valves are easily affected by dirt and debris within the waterway and the thermal expansion (caused by heating the water) creates a higher pressure on the hot water lines. This higher pressure has a tendency to creep into the cold lines and create even larger problems to the domestic water system.
Some alternative designs, such as that shown in U.S. Pat. No. 6,257,493 address this issue by implementing a thermal motor and a cold water bypass mixing chamber that are upstream of the on-off features. However, this design is a single handle design unsuitable for heavy duty applications, is not adjustable, and has high relative manufacturing costs.
There is a need, therefore, for a temperature regulated faucet design that addresses one of more of the above-referenced drawbacks.